1. Field of the Invention
The present invention relates to techniques for monitoring at least one of a plurality of electric power sources in an electric system wherein a load device consisting at least one electrically operated device is electrically connected to the plurality of electric power sources.
2. Discussion of the Related Art
JP-A-10-336915 discloses an electric system wherein a load device is electrically connected to a plurality of electric power sources. In this electric system, the load device can be operated unless all of the plurality of electric power sources are abnormal or defective. Thus, the provision of a plurality of electric power sources in an electric system increases the operating reliability of the electric system.
However, all of the plurality of electric power sources may be defective or abnormal. If it is possible to detect that at least one but not all of the plurality of power sources is defective, it is possible to inform or warn the user of the load device of that fact, that is, that there is a certain possibility that all of the plurality of power sources will be defective. This information or warning help the user of the load device take an appropriate measure or action for the load device, making it possible to avoid undesirable situations which would result from the abnormality of the power source or sources.
The electric current or voltage applied to the load device to which a plurality of electric power sources at least one of which is monitored as a subject power source are connected does not reflect the present capacity or state of each subject subject power source, that is, the ability of the subject power source to energize or activate the load load. To correctly monitor each subject power source, it is necessary to avoid an influence of the other power source or sources on the state of the subject power source.